Connect webmail control panel to domain

I have a email server with a provider which includes the webmail control panel on that requests for my email login.

I would like to be able to access this over my domain ex:

I have tried adding a cname which works, but it only works via http. I would like to have ssl.

I know there are a few ways to do this, but I am unsure the correct way. I do have NGINX setup on my server, so should I use Cloudflare to configure this or NGINX? Thanks

note** I am just using cpanel hosting to host the email. I do have access to that as well